The present invention relates to a process for producing ethylene-.alpha.-olefin copolymers. More particularly, the present invention relates to a process for producing ethylene-.alpha.-olefin copolymers which has no steps of separating the unreacted ethylene and/or dissolved ethylene from a reaction solution, a reaction gas or a mixture of the reaction solution and the reaction gas obtained by an oligomerization reaction and then recycling the unreacted or dissolved ethylene into the oligomerization reaction, and therefore can omit at least the compressor for elevating the pressure and further omit the distillation column for purifying the crude .alpha.-olefin, if desired, and therefore is quite advantageous from the viewpoints of equipment cost and operation cost.
As the general process for producing ethylene-.alpha.-olefin copolymers, there can be referred to the process of oligomerizing ethylene in the presence of an oligomerization catalyst to obtain a crude .alpha.-olefin, purifying the crude .alpha.-olefin to obtain a purified .alpha.-olefin, introducing the purified .alpha.-olefin into a polymerization reactor together with otherwise freshly supplied ethylene, and copolymerizing the .alpha.-olefin and the ethylene in the presence of a polymerization catalyst to obtain an ethylene-.alpha.-olefin copolymer. However, this general process requires a step for separating the unreacted ethylene and/or dissolved ethylene present in the reaction solution, the reaction gas or the mixture of the reaction solution and the reaction gas obtained by the oligomerization reaction and then recycling into the oligomerization reaction, from the viewpoint of economy. For this purpose, at least a compressor for elevating the pressure is necessary, and therefore this general process is not high in efficiency from the viewpoint of equipment cost and operation cost.